Sound 2

Multimedia Authoring

Introduction to Garageband Garageband is both a: • MIDI sequencer • Digital audio recorder

Garageband: Real Instruments • • • •

Tracks displayed in purple, recorded from real instruments Can copy and paste, chop pieces out Cannot transpose them (play back at different pitch) Cannot change tempo (play back faster or slower)

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Multimedia Authoring

Introduction to Garageband Garageband: Software Instruments • Green tracks were created on a MIDI instrument • Can record keyboard performances, display performance bars as a grid (like a piano roll) • Can edit notes, correct mistakes • Drag notes higher or lower • Make them last longer or shorter • Delete unwanted notes • Can transpose a piece (change key so it is higher or lower) • Can speed up or slow down the performance

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Audio File Formats

There are many file formats for storing audio files. It is important to distinguish between file format and codec, even though most audio file formats support only one audio codec, a file format may support multiple codecs. Two major groups - lossless and lossy. •lossless: WAV, PCM, TTA, FLAC, AU, AIFF TTA: 2:1 compression - no data / quality lost in codec •lossy compression: MP3, Ogg Vorbis (OGG), Windows Media Audio (WMA), AAC These are based on psychoacoustic models cutting out sounds we cannot hear - MP3

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Audio File Formats AIFF Audio Interchange File Format (AIFF) •developed by Apple for storing sound in the data fork of Macintosh files Macs use a unique dual-fork file structure - resources in one fork - data in another •not cross platform, not supported by all web browsers •very big •adopted as a standard audio format by the Open Media Format Interchange (OMFI) group for cross-platform media exchange (includes Silicon Graphics, Avid Technology) •GarageBand and Mac-based professional digital audio recording systems - also Audacity import and export •stores audio mono or stereo 16-bit, 8-bit and wide range sample rates •have extension .aif or .iff •there is another format called AIFF-C (compressed) that gives up to 6:1 compression - also AIFC

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Audio File Formats WAV WAVE File Format is a file format for storing digital audio (waveform) data. •supports a variety of bit resolutions, sample rates, channels of audio •Windows native file format for storing digital audio data - vey popular on PC platforms •widely used in professional programs - popularity of Windows •takes into account some peculiarities of the Intel CPU such as little endian byte order low order byte of a number stored at lowest address •almost every program that can open or save digital audio support this format •very useful, flexible •good for storing and archiving original recordings •based on RIFF file format - similar to AIFF •Freeware wav files (http://simplythebest.net/sounds/WAV/sound_effects_WAV/ ) Multimedia Authoring

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Audio File Formats

OGG - compressed Ogg Vorbis is an open, patent-free, professional audio encoding and streaming technology •Open Source •new audio compression format - roughly comparable to MP3 •vorbis - name of the audio compression scheme

http://www.vorbis.com

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Audio File Formats

MP3 - compressed •Uses the MPEG audio layer 3 codec to provide acceptable lossy compression for music files. •compression about 1:10 compared with uncompressed WAV files •MP3 movement an amazing phenomenon - started with a huge audience of music lovers on the Internet, not with the music industry itself •huge impact on how people collect, listen to, and distribute music •some sounds we hear much better than others - if both playing at the same time remove the one our ears ignore

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Audio File Formats

WMA - compressed Windows Media Audio format •Microsoft •Advanced Systems Format (.asf) files •Container format •Specifies structure of audio/video stream •Metadata •Optimized for streaming media

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Audio File Formats

AAC Advanced Audio Coding (AAC) - used by iTunes

Since the 1990s, movie theatres have upgraded their sound systems to surround sound systems. •carry more than two channels •codec copyrighted - encoders / decoders cannot be offered without paying a licence fee •most popular format - 5.1 ( 3 front, 2 back + subwoofer for low frequencies - our ears cannot tell where the low frequencies come from) •Dolby Digital uses a similar codec (AC-3) Multimedia Authoring

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Multimedia Authoring

Bringing an Audio Recording into your Multimedia Project

1. Determine the file formats that are compatible with your multimedia authoring software and the delivery medium(s) you will be using (for file storage and bandwidth capacity) 2. Determine the sound playback capabilities (codecs and plug-ins) that the end user’s system offers 3. Decide what kind of sound is needed e.g. background music, special effects, spoken dialogue Multimedia Authoring

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Multimedia Authoring

Bringing an Audio Recording into your Multimedia Project

4. Decide where and when you want to use either digital audio or MIDI data 5. Acquire source material by creating it from scratch or purchasing it 6. Edit the sounds to fit your project 7. Test the sounds to be sure that they are timed properly with the project’s images. Multimedia Authoring

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Digital Audio

Space Considerations It takes about 1.94 MB to store 11 seconds of uncompressed Red Book stereo sound. Ideas for Reducing Storage Requirements • Is mono sound acceptable? • Use compression • Try downsampling

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Digital Audio

Calculating Storage Needs Sample rate*sample size/8*#seconds*channels =?KB Example You have been assigned to design and produce the audio portions of a multimedia project. The program will be delivered on a CD-ROM, and video clips will take up most of the CD. You have only 50MB of storage space to store 20 one-minute clips of speech, 10 songs averaging three minutes long, and a background sound loop. What sampling rates and depths should you use for the speech, for the music, and for the background sound? Why? Roughly calculate the file size totals for these specifications, and be sure that you end up with less than the 50MB of storage space allotted. Discuss your reasoning. Multimedia Authoring

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Digital Audio

References Vaughan, T. (2011) Multimedia: Making It Work, 8th Ed. , New York: McGraw-Hill Savage, S. (2011) The Art of Digital Audio Recording, Oxford: Oxford University Press

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